Steering mechanism



2 Sheets-Sheet l Aug. 30, 1960 J. w. GooDRlcH STEERING MECHANISM Filed NOV. 24, 1958 Aug. 30, 1960 J. w. GooDRlcH STEERING MECHANISM 2 Sheets-Sheet 2 Filed Nov. 24, 1958 TTMWQ mmm NZTUZU Patented Aug'. 39, 1960 STEERING MECI-IAISM John W. Goodrich, Peoria, Ill., assignor to Le'ourneau- Westinghouse Company, Peoria, lll., a corporation of Illinois Filed Nov. 24, 1958, Ser. No. 775,912 18 Claims. (Cl. 74-720.5)

This invention relates to a steering mechanism, and more particularly to steering mechanism as applied to tractors of the skid-steer type.

There are many skid-steer types of tractors in industry, and this is particularly true of the earthmoving industry. A long standing problem in directional control of skidsteer tractors is that of ability to steer the tractor by small and closely controlled amounts. Too often, the tractor jumps or lurches sideward by an amount which is difficult or impossible to predict by the operator. For tractors moving along a narrow roadway at fairly high speeds, this uncontrollability or unpredictability can be a source of serious trouble. For example, a tractor which is moved along a levee or along a shelf cut into the side of a mountain can easily be plunged over the side if the steering control is such as to cause the tractor to change direction by an unpredictable amount when the operator tries to steer it. This can of course result in injury or death to the operator and in severe damage to the equipment.

It is accordingly an object of this invention to provide steering mechanism for a tractor of the skid-steer type which gives the operator close control of the tractor and is at the same time no physical burden on him. This and other objects are accomplished in a tractor steering mechanism in which provision is made for driving the opposite sides of the tractor at different speeds, the invention providing means to control the diierent speeds at the will of the operator with a high degree of accuracy and with a minimum of physical effort.

In the drawings:

Fig. l is a schematic View showing two ground engaging members of a tractor, the means to drive the ground engaging members, and the steering controls therefor.

Fig. 2 is a View in elevation showing a pair of switches used in the steering mechanism and shown schematically in Fig. 1; and

Fig. 3 is a schematic viewl somewhat similar to Fig. l but showing another embodiment of the steering control.

Referring now to Figs. 1 and 2 for a description of the embodiment there shown, ground engaging members 2 and 4 are shown and it will be understood by those skilled in the art that members 2 and 4 are mounted in any suitable manner on opposite sides of a tractor. The tractor may be one of a number of well-known types. If the invention is applied to a track-laying tractor, then the members 2 and 4 will be the tracks of the machine. However, the invention is not limited to tractors of the track-laying type; indeed, it is here shown as being applied to tractors of the rubber-tired type, as for example a four-wheel rubber-tired type, although the embodiment here illustrated shows only one ground engaging member on each side of the tractor.

The ground engaging members 2 and 4 are driven by an engine 6 which is connected to the ground engaging members by drive means which include a clutch 8 and a change-speeed transmission 10. The output shaft of transmission 10 is shown schematically at 12 and connects with a bevel pinion 14 to drive the pinion. Pinion 14 meshes with a bevel gear 16 which is mounted on a transverse drive shaft 18. At its ends, transverse shaft 18 connects with sun gear shafts 20 and 22l through flexible couplings 24 and 26. Inasmuch as the drive transmission on the two sides are the same, only one of them will be described in detail.

Sun gear shaft 20 carries at its outer end a sun gear 28. Sun gear 28 forms part of a planetary gear train having one or more planetary gears (the drawing shows two) 30 and 32. The planetary gears in turn mesh with a ring gear 34. 'Ihe axes of planetary gears 30 and 32 are mounted on a planet carrier 36 which also serves as a brake drum for a brake here shown schematically at 38. Planet carrier 36 is connected to drive wheel 2'. The planet carrier may be mounted integral with wheel 2 or the two members may be secured together in such a way as to permit a limited amount of relative radial movement while at the same time preventing relative rotary movement. Drives of this nature are old in the art and need not be disclosed here.

Mounted adjacent the planetary gear train just described is another gear train which looks like a planetary gear train but which will here be referred to simply as a gear train because the planet carrier thereof is permanently secured against rotation. More specifically, ring gear 34 is formed integral with another ring gear 40 which meshes with one or more pinions 42 and 44; pinions 42 and 44 are secured against rotation by mounting means 46 and 48, these mounting means being here shown schematically as secured in any suitable manner to some portion of the tractor frame, the axle housing, or the like. A centrally disposed gear 50 meshes with pinions 42 ant 44 and is substantially coaxial with sun gear 28.

As here shown, central gear 50 is formed integral with a shaft 52. Shaft S2 is mounted for rotation in a suitable bearing shown schematically at 54.

Also formed integral with shaft 52 is another gear 56. Gear 56 meshes with an idler gear 58 which in turn meshes with a gear 60. Gear 60 is secured on a shaft 62. At one end of shaft 62, there is provided a brake device 64, and at the other end of shaft `62 there is provided a clutch device 66.

Clutch device 66 permits driving of shaft 62 by means of a shaft 68 on which there is secured a bevel gear 70. A bevel pinion 72 meshes with and drives gear 70. Gear 72 is connected to be driven by engine 6 through a shaft shown schematically at 74. Shaft 74 is schematically shown as passing straight through change speed transmission 10. This is intended to indicate that shaft 74 is not aected by gear changes. Instead, for any given engine speed, shaft 74 runs at a constant speed so long as clutch 8 is engaged.

Reference was made above to the clutch device 66 which permits driving of shaft 62 by shaft 68. A second clutch device 76 is mounted at the opposite end of shaft 68 and enables shaft 68 to drive a shaft 78 on which there issecured a gear 80. Gear 80 is associated with ground engaging member 4 in the same manner that gear 60 is associated with ground engaging member 2. A brake device 82' is also secured to shaft 78.

The drive mechanism described above is fully disclosed and claimed in copending application Ser. No. 560,964 of Ralph B. Clark and Ernst W. Spannhake, liled January 24, 1956, and assigned to the assignee of this application.

Actuating means are provided for the clutch and brake devices 66, 76, and 64, 82 referred to above. In the embodiment shown, the brake devices are designed to be normally engaged while the clutch devices are designed to be normally disengaged. Toward that end, springs 84 are disposed to engage the brake devices, and springs 86 are disposed to disengage the clutch devices. In nthe embodiment shown, the actuating 4means are fluid pressure operated.. lMore specifically, Vt-he actuating means consist of pneumaticmotors. Thus, the `actuating means `8.8'for .brake device 64 consists of la pneumatic motor having ,acylinder `90, aipiston 92, ,and `a 'piston rod 94,rod .94 being connected with the brake .shoe of Ythe Ybrake deviceY 164,. It will Vof-.course beY understood Vby those skilled in the -art that `.the showing here is purely NSchematic. Furthermore Yit will Yalso .be ,understood that the spring 84 may be disposed where the Udesigner sees lit .to put it. 'For reasons ofconvenience, the springs 84 .and v8.6 are here shown .as located within the pneumatic cylinders. Actuating means 9 6 .is shown connected to operate brake Adevice -82. Actuating means 98 is shown .connected to operatev clutch .device ,66, and actuating means 100 -is Yshown connected to operate ,clutch device76.

viewof the statement ,above to the eiect that the brake devices are normally engaged .and the clutch devices are normally disengaged, it will be understood that the fluid pressure connections ,are ,such that the admission of fluid under pressure to a `brakeadevice serves to disengage the brake, while theadmissionof duid under pressure to a clutch device serves Vto engage .the clutch. AForethat purpose, uid pressure connections 102, 104, 10,6, and 108 are provided for the clutch and brake 4device actuating means 88, 98,100, and 96 respectively.

Fluid under pressure is supplied to the aforementioned i uid pressureconnections by means of a pressure line 110 which receives uid under pressure from a tank 112.

"Tank y112 -is supplied with fluid under pressure by a suitable pump 114 through a lter 116 and a conduit 118. vPump 114 is connected to be driven by engine 6 through any suitable conventional drive, here `shown schematically at 120. Y

The actuating means are electrically controlled in the embodiment shown. Forthat purpose, valves122, 124, 126, and 128 are shown in the fluid pressure connections `102, 104, 106, and 108'respectively. As here shown, these valves are or" course purely schematic, .and Yeach valve is provided with a straight through passage 130 and an exhaust passage 132. Y

yIt may be pointed out here that ,the exhaustpassages .for valves 122 and 128 are considerably smaller than the exhaust passages for the valves v124 and'126. Thepurpose of this dilerence is to provide a time delay in the application'of the brakes of vrdevices 64 and 82. Similarly, orices 134 and 136 are provided in the iluid pressure connections 104 and 106 in order to provide a time delay in the application of the clutches of devices 66 and 76. Y .Y Y

The aforesaid valves `122, V124, 126, and 128 are .connected to be electrically operated. Thus, a solenoid 138 having a coil 140 and an armature 142is connected to operate valve 122. Similarly solenoids 144, 146, and 148 are connected to operate valves 124, 126, and 128 respectively.

Operator-operable means are provided lto -control the solenoids 138, 144, 146,`and 148. A source of electric power such as a storage battery 150 is provided to furnish the electric power necessary to operatethe solenoids. The battery 150 is preferably the storage battery which is conventionally used in tractors of'this type; One terminal of the battery is grounded as shown at 152. The otherterminal of the battery lis connected by aconduit 154 with a double-pole double-throw switch 156. A `simple on-olf switch 158-1is provided in conduit' 154; switch 158 can be connected to be turned on and otiewith the ignition of engine 6.` Alternatively, a separate and diierent lock maybe provided for switch 158, as will heunderstood by those skilled in the art. Switch 156 is one of a number kof control switches in the over-all electrical contrclrmeans of the tractor steering mechanism. In addition to switch 156, there is shown in Fig. l a pair of switches 160, 162 and a second pair of switches 164, 166. Each of the `switches 160, 162, 164, and 166 is preferablyof a type disclosed in Patent 2,629,791, LeTourneau, dated February 24, 1953. The switches 160, 162 are preferably mounted with their operating plungers opposed to eachother -as shown at 168 and 170 respectively. An operating lever 172 is disposed between the endsY of plungers,l 168 Vand 170.

As is best seen in Fig. 2, the switches `are preferably mounted on any suitable panel. The operating lever 172 is pivoted `at 174V so that movement ofethe upper end of lever 172 to the Yleft as Vseen in Fig. 2 serves to operate the switch on the right, namely'switch 162. Moreover, it will be noted that such movement of the upper end of lever 172 to the left moves the lower end of the lever away from switch `160. Accordingly, .movement of lever 172 kto operatefswitch 162V necessarily `.excludes the operation of switch 160.V Similarly, -with this arrangement, Vtheoperation .of switch l -by lever 172 would eXcludethe operation of switch 162.` i- Y Switches 164 and -166 may be mounted in a manner similar to switches .160 and -162. Accordingly,Y the mounting of those switches ineed `not Vbe-;discussed in detail here. Y YInasmuch as switches .160, 162,Y 164, and 166V 'are substantiallyalike, it will suce to describeone of them. Moreover, because the structure of one of these switches Iis shown in detail in the above-identiiied LeTourneau patent, it will not be necessary to describe the switches here-in any great deta-il.

Each of the switches `providesa normally closed circuit and a normallyfopen circuit. Thus, switch 160 has four fixed contacts 176, 178, 180, and 182. A movable .bridging contact 184 is provided. As will beseen from a consideration of the above-identiiied patent, the bridgf ing contact 184 moves with a snap action, being arrovercenter device. As switch 160 is shown in Fig. 1, .the normally closedcircuit consists of iixedecontact 176, bridging contact 184, and xed vcontact-178, while `the normally open circuit consists .of xed contacts and 182. Actuationof the plunger 168 operates the over center device so that `bridging contact 184 dis'engages itself from Iixed contacts 176, .178,and engages fixed contacts 180, 182. f l Y 'c Y' Switch 156 is connected vwith the first-named pair of switches 160, 162 by means of a conduit 186 connecting contact'188 with contact176and conduit 190 connecting contact 192 with -a Vfired Vcontact 194 of'switch n162, contact 194 corresponding to contactV 176 ofswitch1160. The connection of switch 156 with switches 160,162 just described is withV the normally closed-circuit of those switches. Switch 156 `is -also'connected with :the normally open circuits of those switches. This connection is ac'- complished by a conduit 196 connecting-a contact 198 of switchr156 with contact 3180 of switch 160. A-conduit 200 connects a 1contact'202 of switch'156 with a contact 20'4 of switch `162, contact 204 corresponding to contact 180 ofswitch160. f The normally closedV circuit of each .of switches 160, 162 is connected to control the drive means of one ground engaging member-,while Vthe normally opencircuit of the switch is lconnected ,tocontrol lthe diive'means of the other groundr engaging member. 'In' the Vembodiment shown, these connections are accomplished through the second-named pair of switches 164,166'.

More speciicaIly, the normally closed circuitcf switch 169 includes xed contact "178. A conducit `206fiscon nected with fixed contact 178 and with another conduit 208, conduit 208connectinga xedcontact of switch 1627with Va Vlined contact 212 of switch166. Ajurnper connection V214 connects iixedcontact 2 12of switch` 166 :with a fixed contact 216 of the same switch 166. A con-V duit 218 connects at its one end with xed contact 216 and at its other end with one end of coil 140, the other end of the coil being grounded as shown at 220.

The aforementioned conduit 208 connects the normally open circuit of switch 162 with switch 166 and solenoid 138 as will by now be understood by those skilled in the art from the foregoing description.

The normally open circuit of switch 160 is connected with the normally open and the normally closed circuits of switch 164. To accomplish this connection, a conduit 222 connects iixed contact 182 of switch 160 with a iixed contact 224 of switch 164. A jumper connection 226 electrically joins the xed contact 224 of switch 164 with a xed contact 228.

The normally closed circuit of switch 162 is connected with switch 164; thus, a xed contact 230 of switch 162 is connected with conduit 222 by a conduit 232. Thus the normally closed circuit of switch 162 is connected with switch 164 and with the controls for the actuating means associated with the drive means for ground engaging member 4.

To accomplish this connection7 a conductor 234 is connected at its one end to fixed Contact 228 of switch 164 and at its other end is connected with one end of the coil of solenoid 148. The other end of the coil being grounded as shown at 236. Another xed contact 238 of switch 164 is connected with one end of a conductor 248 of which the other end is connected with the coil of solenoid 146. The coil is grounded as shown at 242. The iixed contacts 228 and 238 form, with a bridging contact 244, a normally closed circuit of switch 164.

In like manner, switch 166 is connected with solenoid 138 as detailed above. Another xed contact 246 of switch 166 is connected to one end of a conductor 248 of which the other end is connected with the coil of solenoid 144; the coil is grounded as shown at 250. Fixed contacts 216 and 246 of switch 166 form, with a bridging contact 252, a normally closed circuit for switch 166.

Switches 164 and 166 also have normally open circuits. Fixed contact 224 of switch 164 and a iixed contact 254 form the normally open circuit. As for switch 166, fixed contact 212 and a tixed contact 256 form a normally open circuit. A conductor 258 connects the xed contacts 254 and 256. A conductor 260 connects ixed contact 254 with switch 156 and, through switch 156, with conductor 154 and battery 150.

An operating lever 262 is disposed between switches 164 and 166 in much the same manner as operating lever 172 is disposed between switches 160 and 162.

The embodiment of Figure 3 Reference will now be had to the embodiment shown in Fig. 3. The description of this embodiment will be concerned only with the diiierences between the two forms which the invention takes.

Whereas the embodiment shown in Fig. l controls the switches 164 and 166 by the same manual means as is provided for the switches 160 and 162, in the embodiment shown in Pig. 3, diiierent means are provided to control the second pair of switches.

In the Fig. 3 embodiment, .the second pair of switches is shown at 364 and 366, these switches being adapted to be operated by levers 461 and 462, these levers being pivotally mounted on any convenient portion of the frame. Lever 461 is connected to actuate the bridging Contact 444 of switch 364, and lever 462 is connected to actuate bridging contact 452 of switch 366.

Switches 364 and 366 are connected with the rst pair of switches 368 and 362 in much 4the same manner as in Fig. 1; however, the physical orientation of the switches diiers somewhat because of the means of control, and as a result the connections appear to be different.

Fixed contact 378 of switch 360 is part of the normally closed circuit of that switch and is connected with both circuits of switch 366. To accomplish this connection, a conductor 406 is connected with xed contact 416 by way of a portion of conductor 418. The connection also goes to xed contact 412 by way of the jumper connection 414. It will be recognized lthat; the normally closed circuit of switch 366 comprises iixed contact 416, bridging contact 452, and xed contact 446. The normal- 1y open circuit of switch 366 comprises the aforementioned fixed contact 412 and another xed contact 456. The normally open and normally closed circuits of switch 366 are connected with iixed contact 410 of switch 362 by means of conductor 408.

The normally closed circuit of switch 362 is connected with both circuits of switch 364. To accomplish this connection, fixed contact 430 of switch 362 is connected by a conductor 432 with fixed contact 428 of switch 364 by way of a portion of conductor 434, and it is also connected with xed contact 424 by way of the jumper connection 426. Fixed contact 424 is connected with the normally open circuit of switch 360 by the connection of conductor 422 with tixed contact 424 of switch 364 and fixed contact 382 of switch 360.

Switch 364 is thus provided with a normally closed circuit and a normally open circuit, normally closed circuit comprising xed contact 428, bridging contact 444, and iixed contact 438; the normally open circuit comprises xed contact 424 and iixed contact 454.

The normally open circuits of switches 364 and 366 are connected with switch 356 by means of the connection of iixed contacts 454 and 456 with conductors 458 and 460, and through switch 356, with conductor 354 and power source 350.

The remainder of the embodiment shown in Fig. 3 is sufficiently similar to that of Fig. l to require very little additional description. Thus, the aforementioned conductors 418 and 434 are connected with solenoids 338 and 348 respectively, these being the solenoids which control brake devices 264 and 282 respectively. In addition, one end of a conductor 448 is connected with ixed contact 446, and the other end of the conductor is connected lwith solenoid 344; and one end of a conductor 440 is connected with iixed contact 438, while its other end is connected with solenoid 346. Solenoid 344 controls clutch device 266, and solenoid 346 controls clutch device 276.

' Operation Reference will be made to the embodiment seen in Fig. 1 for a description of the operation. The gear trains shown to drive a ground engaging member are so arranged that the drive axle is in the high range when brake devices 64 and 82 are engaged. In these circumstances, ground engaging member 2 is driven by the planet canier 36, the axes of planet gears 30, 32 revolving about the axis of sun gear 28. Sun gear 28 is driven by engine 6 through change-speed transmission 10 at the gear ratio selected by the operator. Ring gear 34 is stationary because it is integral with ring gear 40 and ring gear 40 is held against rotation under these circumstances because gear 56 is held against rotation by brake device 64.

If now the brake device 64 is disengaged and if clutch device 66 is engaged, gear 56 will be rotated through the power train shown. The rotation of `gear 56 is such as to slow down the rotation of planet carrier 36, as will be understood by those skilled vin the art. It will of course be understood that the amount that planet carrier 36 is slowed down will depend upon the gear ratio selected by the operator as he manipulates transmission 10, inasmuch as the rotational speed of shaft 7 4 is not affected by gear changes lselected by the operator. In other words, in the lowest gear selection for transmission 10, the rotation of ring gear 34 will come close to offsetting rotation of planet carrier 36.

The power train which drives ground engaging memrange.

ber 4 is the same as the power train for member 2, so no attempt 'will be made to describe the operation of the drive for member 4 in detail.

VLet it be assumed that the vehicle is moving forward and that the forward motion is to the right asseen in Fig. l. Let it be further assumed that switch 156 is closed so that Ycontacts 188 and 192 are engaged. It is valso assumed that switch 158 is closed. Under these conditions, power is supplied to all four solenoids.

More specifically, looking rst at the circuit for switch 160, the Vcircuit is traceable as follows: power source G, conductor 154, switch 156, conductor-186, the normally closed circuit of switch 160,V conductor 206,V conductor 208,'theV normally closed circuit of switch 166, and conductorsV 218 and 248 to solenoids 138 and 144'respectively. Similarly, completed circuits can be traced through switches 162 and 164 to solenoids 146 and I148.

With all of the solenoids energized, valves 122, 124, 126, and 128 are operated to admit fluid under pressure to the air motors 88, 98, 169, Vand 96 respectively.

Brake devices 64 and 82 are thereupon released or disengaged', while clutch devices66 and 76 lare engaged. It should `be noted that there is no impediment to the immediate operation of the 'brake devices. However, the orifices 134 and 136 serve to delay the operation of clutch devices 66 and 76, in order to insure that the brake devices are fully disengaged before the clutch devices are engaged.V

With all of thesolenoids energized, the drive axle oper- `ates in the lowrange. Let it now Ybe assumed that the operator 'wishes to steer the vehicle to the left. Referring now to Fig. 2, note that the operator moves the handle 172 to the left as seen in Fig. 2. Inasmuch as switch handle 172 is pivoted at 174, switch l162 is engaged by this manipulation.

Referring now again to Fig.V l, it will be noted that the operation of switch 162 interrupts the normally closed circuit of that switch, interrupting the ofw of power to switch 164 and solenoids 146 `and 148.Y With these two solenoids deenergized, Ivalves 126 and 128 return tothe position shown in the drawing. Spring 86 disengages clutch device 76 and spring 84 engages `brake device 82. It may be noted however that the exhaust port in valve 128 is quite restricted, and the purpose of this is to insure that the application of brake device 82 will be delayed until clutch device 76 has become fully disengaged.

Under these conditions, the drive for ground engaging member 4 is shifted into the high range.V The drive for ground vengaging member 2 continues in the `low range. With ground engaging member 4 running faster than ground engaging member- 2, the vehicle steers to the Ileft. Steering of the vehicle tothe right will easily be understood by those skilled in the art from the above description and will not be detailed here. Y

Let it now be assumed that switch 156 is manipulated to engage xed contacts 198 and 262. In this operating position of switch `156 it will be noted that there is no voltage applied to the normally closed circuits of switches 160 and 162. Instead, voltage is applied to the normally open circuits of those switches by fway of conductors 196 andrZG. However, with switches 168 and 162 in their normal operating positions as shown in Fig. 1, the circuits `are open-so the application of voltage to contacts 180 and 2914 accomplishes nothing at this time.

`With switch 156 engaging fixed contacts 198 and 202, all of the solenoids are de-energized and the parts assume the operating position shownin-Fig. l. As -will be understoodfromV the above explanation, the drive axle is now in high range.

VLet it now be assumed lthat the operator wishes to steer the vehicle while the driving axle is in high speed Again let it be assumed that he wishes to steer to the left. Again, switch 162 is operated so that the bridging contact forms a closedA circuit of the fixed contacts 204 and 2,10.V There isV then' ah electric circuit as follows: power source'150, conductor 154, switch 156, conductor 200, contactsY 204 and 210 of switch 162, Vconductor 20S, switch 166, `and conductors A2`1`8ai1d`248 to solenoids 138 [and 144'respectivelyl With solenoids 138 and 144 energized, lthe drive means for ground engaging member 2 -is shifted from the high range'it'was in, to the low range as is explained above. inasmuch as 'ground engaging member 4 continues in the high range, member 4 runs faster than member 2, and the vehicle steers to the left. y v

Steering of the vehicle to the right under these conditions will be understood from the foregoing and need not be set forthindetailhere. Y V

The steering operations thus far described rare for what is sometimes called power steering because it is accomplished by actually `Ydriving the outside wheelY at a higher rate of speed than the drive for the inside wheel. As shown here, the invention provides still another method of steering, called skid-steering because the inside wheel is completely disengaged from its drive sothat it may be braked. Skid-steering is accomplished through the yswitches 164 and 166 by means of the operating handle 262. inasmuch -as switches 164 and 166 are mounted in relation to handle 262 in much the same manner as the switches shown in Fig. 2, it will of course be understood that movement of handle 262 upward as seen in YFig. l will operate switch 166. Accordingly, let it be assumed that switch 166 is thus operated in order to steer to the left. What happens is that the normally closed circuit of switch 166 is broken and a` circuit is established across fixed contacts 212 and 256. When the normally closed circuit of switch 166 is broken, iixed contact 246 is isolated so that, no matter what the operating condition of the vehicle is otherwise, conductor 248 is dead and solenoid 144 is de-energized; the result is that clutch device 66 is disengaged-whether it was previously engaged or not. Meanwhile, a circuit is provided for solenoid 138 as follows: power source 154i, conductor 154, the jumper of switch 156, conductors 260 and 258, contacts 256 and 212 of switch 166, and conductors 214 and 218 to the coil of solenoid 138. As a result, solenoid 138 is energized regardless of its condition before the operator manipulated handle 262. As a consequence of the manipulation of handle 262 justV described, solenoid 138 is energized to release brake device V64 but solenoid 144 is de-energized to disengage clutch device 66, with the result that there is no reaction member for the gear train which comprises pinions 42 and 44. The necessary consequences of this condition is that the drive for ground engaging member 2 is completely disconnected. The operator is thereupon free to engage brake 38 with the planet carrier 36 to stop ground engaging member 2 and accomplish `what is known as skid-steering because ground engaging member 4 is still connected. The vehicle thus steers to the left. Y

Skid-steering of the vehicle to ythe right is of course simil'arto the steering operation to the left just described, so it is not necessary to go into detail on the method of the steering to the right. Y Y

The operation of the embodiment shown in Fig. 3 is substantially the same as the operation just described of the lerltlodi'.ment shown in Fig. l, except that the skidsteering switches 364 and 366 are operated by means of separate levers 461 and 462 respectively. Skid-steering of the embodiment shown in Fig. 3 is accomplished by individual manipulation of Vlever 461 or lever 462, at the will of the operator. There is one feature of the Fig. 3 embodiment which is not present in the Fig. 1 embodiment. Whereas only one of the two switches 164 and 166 can be actuated at a time, the corresponding switches 364 and 366 in Fig. 3 may be actuated simultaneously to permit complete disengagement of the vehicle drive by means of the steering switches. In some conditions of operation, this feature may have a definite advantage.

It will be evident from the foregoing that the invention provides steering mechanism for a tractor or other vehicle which gives the operator close control but without imposing any physical burden on him. Other advantages will be apparent to those skilled in the art.

While there are in this application specifically described two forms which the invention may assume in practice, it will be understood that these forms are shown for purposes of illustration and that the invention may be modified and embodied in various other forms without departing from its spirit or the scope of the appended claims.

What is claimed is:

1. Steering mechanism for la tractor having a ground engaging member at each side thereof, the means to drive each ground engaging member in a high speed range and a low speed range, comprising electrically controlled actuating means to connect a drive means in either speed range, a pair of switches, `each switch having a normally closed circuit connected to control the drive means of one ground engaging member and a normally open circuit connected to control the drive means of the other ground engaging member, means selectively to apply voltage to the normally closed circuits of the pair of switches or the normally open circuits thereof at the will of an operator, and means to operate the pair of switches.

2. Steering mechanism as in claim 1, in which the lastnamed means is operable to operate either switch to the exclusion of the other. v

3. Steering mechanism as in claim 2, and another pair of switches each of which has a normally open circuit and a normally closed circuit, each of said other pair of switches having a connection with a circuit of each of the rst-named pair of switches.

4. Steering mechanism as in claim l, and another pair of switches each of which has a normally open circuit and a normally closed circuit, each of said other pair of switches having a connection with a circuit of each of the iirst-named pair of switches.

5. Steering mechanism -as in claim l, and another pair of switches each of which has a normally open circuit and a normally closed circuit, each of said other pair of switches having a connection with the normally open circuit of one of the first-named pair of switches and with the normally closed circuit of the other of the iirst-named pair of switches.

6. Steering mechanism as in claim 1, and another pair of switches each of which has a normally open circuit and a normally closed circuit, each circuit of each of said other pair of switches having a connection with the normally open circuit of one of the first-named pair of switches and with the normally closed circuit of the other of the rst-named pair of switches.

7. Steering mechanism for a tractor having a ground engaging member at each side thereof, and means to drive each ground engaging member in a high speed range and a low speed range, comprising electrically controlled actuating means to connect a drive means in either speed range, a switch having high speed and low speed operating positions, a pair of switches connected with the rst named switch and with the electrically controlled actuating means and each switch of the pair providing a pair of circuits and corresponding operating positions to make or break those circuits, and means to operate the pair of switches to steer the tractor.

8. Steering mechanism for a tractor having a ground engaging member at each side thereof, and means to drive each ground engaging member in a high speed range and a low speed range, comprising electrically controlled actuating means to connect a drive means in either speed range, a switch having high speed and low speed operating positions, a pair of switches connected with the rst-named switch and with the electri- 10 cally controlled actuating means and each switch of the pair providing a pair of circuits and corresponding operating positions to make or break those circuits, and means to operate one of the pair of switches to the exclusion of the other to steer the tractor.

9. Steering mechanism for a tractor having a ground engaging member at each side thereof, and means to drive each ground engaging member in a high speed range and a low speed range, comprising electrically controlled actuating means to connect a drive means in either speed range, a switch having high speed and low speed operating positions, a pair of switches connected with the rst-named switch and with the electrically controlled actuating means and each switch of the pair providing a normally closed circuit and a normally open circuit and corresponding operating positions to make or break those circuits, and means to operate the pair of switches to steer the tractor.

10. Steering mechanism as in claim 7, and a second pair of switches connected with the drive means and with the lirst-named pair of switches, each switch of the second-named pair providing a circuit operable to control disconnection of one of the ground engaging members from its drive means, and means selectively to operate one of the second-named pair of switches.

ll. Steering mechanism for a tractor having a ground engaging member at each side thereof, and means to drive each ground engaging member including a clutch device and a brake device, comprising: electrically controlled actuating means for each device; a pair of switches, each switch having a normally closed circuit connected to control the devices of one drive means `and a normally open circuit connected to control the devices of the other drive means; means selectively to apply voltage to the normally closed circuits of the pair of switches or to the normally open circuits thereof at the will of an operator; and means to operate the pair of switches.

l2. Steering mechanism as in claim 11, and a second pair of switches, each switch having a normally open circuit and a normally closed circuit connected in parallel; means connecting the second pair of switches with the devices; other means connecting the parallel circuits of each switch with the normally open circuit of one of the rst-named pair of switches and with the normally closed circuit of the other of the first-named pair of switches; and means to operate the second pair of switches.

13. A tractor having a ground engaging member at each side, drive means for each ground engaging member including a brake device and a clutch device whereby engagement of one device and disengagement of the other permits drive of the associated ground engaging member in a low speed range or a high speed range depending upon which device is engaged and which is disengaged by the operator, and a stopping brake for each ground engaging member, the invention comprising: electrically controlled actuating means for said devices; a switch having high speed and low speed operating positions; a pair of switches connected with the rst-named switch and with the actuating means, each switch of the pair providing a pair of circuits and corresponding operating positions to make or break those circuits; means to operate the switches to control steering of the tractor by permitting the driving of one ground engaging member faster than the other; a second pair of switches connected with the actuating means and with the first-named pair of switches, each switch of the second-named pair providing a circuit which controls disconnection of one of the ground engaging members from its drive means to permit steering by braking the disconnected ground engaging member; and means to operate the secondnamed pair of switches.

14. A tractorl having a ground engaging member at each side, and drive means for each ground engaging member including a brake device and a clutch device 11 whereby engagement of one-device and disengagement of the other drives the associated ground 'engaging member in1alowspeed ran'geor'ahigh speed range'dep'ending upon which devic'eis engaged and which is disengaged by the operator, the invention comprising: electrically controlled actuating means for said devices; a switch having high speed and low speed operating positions; a pair of switches connected with the first-named switch and withthe actuating means, each switch of the pair pro-V viding a pair of circuits and corresponding operating positions to'make orV break those circuits; and means to operate the switches to steer the tractor by driving one ground engaging member fasterthan the other.

15. A tractor having a ground engaging member at each side, drive means lfor each ground engaging member including a normally engaged Vbrake device and a normally disengaged clutch device whereby engagement of one device and disengagement ofthe other drives the associated ground engaging member in a low speed range or a high speed Yrange depending upon which device is engaged, uid pressure operated actuating means to disengage each brake and engage each clutch, a sourceV of electric power, a switch having high speed and low speed operating positionsvand connected to the power source, a pair of switches connected with the first-named switch and with the fluid pressure operated actuating means and eachA switch of Vthetpair providing a pair of circuits and corresponding operating positions to make or break those circuits, and means to operate the pair of switches to steer the tractor.

' 16. A tractor as in claim 15, a stopping brake for each ground engaging member, a second pair of switches connected with the first-named pair of switches and with the actuating means, each switch of the second pair providing a circuit operable to cause disconnection of one of the ground engaging members completely from its drive means, andmeans selectively to operate one of the second pair of switches to permit steering by braking the disconnected member. t

17. A tractor having a ground engaging member at veach side, drive means for each 'ground engaging member including a--brake device and a clutch device whereby engagement of one device and disengagement of the other drives the associated ground engaging memberriu a low'speed vrange or a high speed range depending' upon which device is engaged, fluidpressure operated' actuating means to operate the brake and'clutch devices, a source of electric power, a switch having high speed and low speed operating positions and connected to the power source, a pair of switches connected with the lirst-named switch and withv the iluid pressure operated actuating means and each switch of the pair providing a normally closed vcircuit* connected with the actuating means for the clutch and brake devices associatedwith one drive means and a normally open circuit connected withV the actuating means for the clutch and brake devices associated with the other drive means and havingvv corresponding operating positions to Vmake or break 'those circuits, and means to operate the pair .of switches to control steering of the tractor.

18. A tractor as in claim 17, a stopping brake for each ground engagingtrnember, a second pair of switches connected with the rst-,named pair of v-switches and with the actuating means, each switch of the second pair providing a circuit operable to control disconnection of one of the ground engaging members completely from its drive means, and means selectively to operate one of the second pair of switches to permit steering by braking the disconnected member. t

References Cited in the iile of this patent UNITED STATES PATENTSV 2,583,065 Stephan Jan. 22, 1952 2,655,054 Kelley Oct. 13, 1953 2,689,488 Storer et al.- v Sept. 21, 1954 2,706,419 K'elbel Apr. 19, 1955 2,757,513 Banker Aug. 7, 1956 2,781,858 Kelley Vet al. Feb. 19, 1957 2,795,963 Alfieri June 18, 1957 UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No. 2,950,633 August SO, 1960 .Iohn W.. Goodrich It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the drawings, Sheet 2, Fig, 3, the conduit shown at the tsp oi Fig., 3 is broken or interrupted and sh0u,ld be shown as one continuous Conduit; in the printed specification, column 2, line 55, for "ant" read and column 9, line I6, Tor "the" .read and Signed and sealed this 25th day of April l96l ERNEST W SWIDER DAVID L, LADD Attestng Officer Commissioner of Patents 

